Use of a modem, e.g., incorporated in a personal computer, to access the Internet and other on-line services to obtain information is ubiquitous. The on-line access, especially from home, is typically achieved via a plain old telephone service (POTS), where a telephone line comprising a pair of copper wires provides a two-way communication path between the modem and a central office (CO). The latter connects the modem to a specified on-line service provider through a public switched telephone network (PSTN).
In an on-line access connection, uplink traffic from a modem to a CO typically contains requests for information, which does not require much bandwidth. On the other hand, downlink traffic from the CO to the modem typically contains the requested information for downloading, which requires significantly more bandwidth. Based on this observation, telephone companies are introducing new services, including an asymmetric digital subscriber line (ADSL) service, which permits fast on-line access. For example, the ADSL service supports uplink traffic having a maximum bit rate on the order of 1 Mb/s, and downlink traffic having a maximum bit rate on the order of 10 Mb/s. For economic reasons, the ADSL traffic traverses the same copper wire pair traditionally used as the telephone line in the POTS.